From the brain's point of view, What is humor when something is funny? Why do we breathe in and out rapidly? Do other animals laugh? Why do most jokes come in threes? What do mystery novelists, magicians and comedians have in common? And could AI be truly funny? Welcome to Inner Cosmos with me and David Eagleman. I'm a neuroscientist and author at Stanford and in these episodes we sail deeply into our three pound universe to understand why and how our lives look the way they do. Today's episode is about humor. Although humor is one of the most valued aspects of our lives, you've probably heard very little about it from the scientific point of view, and that changes today. So why do we laugh? After all? It's very strange behavior. Imagine that you are a space alien and you are studying humans. So through years of study, you note that humans seem to have a relatively high bandwidth channel of communication by an extraordinarily rapid and precise use of their larynx and their vocal cords. They move their tongue and their lips very rapidly. They blow air at just the right moments, and in this way they have language. They communicate to each other at about thirty nine bits per second, which is a pretty good transmission rate and way higher than any other animal species as far as you the alien can tell. But there's something else. These human creatures do something that's very strange. Every once in a while, they do a much lower frequency, lower bandwidth thing where they make a series of rhythmic, involuntary contractions of their diaphragm, which causes a sequence of vocalized exhalations, usually a series of short repeated vowel sounds like ha or he or ho. Now, you notice that this typically begins with some language or event that triggers the brain's reward centers and lights up something about the emotional networks, and that triggers the activation of facial muscles, particularly around the mouth and eyes, And often the human's mouth will open up wide and the corners of the lips will get drawn back and upward, and the respiratory starts doing these rapid cycles of inhalation and exhalation, which throws a wrench in the normal breathing patterns, and the heart rate increases and the blood pressure rises, and the eyes might start to produce tears, and the skin around the face might start turning red because of the increased blood flow. Sometimes the whole body shakes or quivers, especially in the shoulders and torso, and this physical manifestation that can spread to the limbs, leading to movements like clapping or slapping or bending over. Now, the question you ask as the alien is why do they do this strange laughing thing? Is there an evolutionary reason behind it? Do any other animals on the planet do it? So you go back to your alien university to present your findings, and the faculty there drills you with questions that you're supposed to know the answer to, like why do humans go to clubs and movies with the hopes that they will trigger a lot of these diaphragm contractions And if they get fewer contractions than expected, do they seem disappointed? Why do they get together with other humans that they trust to stick food in their mouths and hope to do these strange diaphragm contractions while eating, even though it's dangerous and could cause them to choke on their food. So we're going to take this in a few acts. First, we're going to address what is humor, And in the second act we'll ask why do we laugh? In other words, why do we do it out loud instead of silently. So let's start with the general notion of comedy about something being funny. As it turns out, people have been wondering about this for a long time, and the first known theories about humor go back to Plato. Now, Plato had a very dim view of laughter. He generally saw it as something malicious that people do. In his view, audiences laugh at people who have ignorance about themselves, who imagine themselves to be richer than they are, or better looking than they are, or more virtuous than they are, and we laugh at them, which he found to be a morally objectionable thing to do. Now, his student Aristotle appreciated wit in conversation, but he agreed with Plato that people laugh at the misfortunes or mistakes of others, which reinforces their own sense of self worth and status. Think of an audience laughing at a character in a comedy who's consistently making foolish mistakes. So this is what's known nowadays as superiority theory, and the idea is that comedy stems from feelings of being better than other people, and no one really challenged this idea that that's what comedy was about. Until the mid eighteenth century people started to think, wait a minute, you don't really need feelings of superiority to laugh at something. Just think of a funny poem or pun. And on the flip side, we often feel superior, like the way you might feel superior to a horse or a squirrel, but that doesn't mean we laugh at them. So other theories began to blossom, and now there are many theories of humor. One of them, for example, is relae theory. This was originally proposed by A Lord Shaftsbury in the seventeen fifties, and he suggested the slightly strange idea that we laugh to release animal spirits that have built up inside us. Now, this doesn't make much sense in our modern vocabulary, but later proponents of this idea, like Sigmund Freud and Herbert Spencer, they cast this same idea in a different light. They said, look, humor is a way to release psychological tension or suppressed emotions, like think of laughing at a joke that touches on a taboo subject. So laughter serves as a release valve for pent up energy in your nervous system, and in this view, it's a purely physiological issue. And you see this happen sometimes when someone laughs at a totally inappropriate moment, like someone has died, and the excess energy comes out in a way that looks different from what they're feeling internally. Relatedly, by the way, Freud also suggested that humor and laughter might act as a defense mechanism, and in this way it allows people to deal with uncomfortable emotions or social tensions, and it can reduce stress and anxiety. But there are other ways that people look at humor. One very common school of thought looks at humor as a way of indicating play. It says, look, play is absolutely essential for learning how to do real things in the world. And so the idea is that humor engages all this cognitive practice and social practice in a playful context. For example, look at the way that children engage in silly wordplay or crazy imaginative scenarios. That stuff cracks them up. They're playing. And there's a closely related way of looking at this too. When that evolutionary psychologists like the idea that humor and laughter is all about social bonding. Humor is a tool for strengthening the bonds within a group. You build cohesion this way, you build a sense of community. So just think about inside jokes that you do with your friends that reinforce your group identity and your camaraderie. And I think that the slang that each generation introduces is a form of the same thing, making sure that the adults are on the outside and you and your pals are on the inside. It's a way of bonding. Now, the ideas about humor don't end there. Other thinkers like Marvin Minsky and Jerry Saul's focus on a different aspect of humor, the cognitive aspect. They care about the mental processes involved in understanding and appreciating comedy. So they're looking at the cognitive effort required to understand some cognitive play on words. So take a joke like this today. I found a book with the title how to Solve fifty of Life's Problems, So I bought two of them. So the last sentence comes as a surprise, and the brain goes back and tries to reinterpret what it heard. There's a puzzle in there. Which forces you to reshape your interpretation, or specifically, your interpretation of the speaker's interpretation. And then it falls into place that there's another way to see this, and it strikes us as funny because it's both nonsensical and a little bit sensical. And some other theories zoom in even more on the types of humor that have to do with linguistics, in other words, about the structure and use of language, like wordplay or jokes that rely on double meanings like I'm addicted to break fluid, but it's okay because I can stop at any time, or jokes that rely on homophones, like a photon checks into a hotel, the front desk asks if it has any luggage and it says, no, Oh, I'm traveling light. So the punchline is a phrase that can be reinterpreted and has two meanings that surprisingly fit. Now, fundamentally, your brain is always trying to squeeze the complexity of the world down to a single interpretation. And something about the back and forth here between two interpretations that can both work makes something funny. Or take a kid's joke like why aren't lobsters generous because they're shellfish? This relies on two sounds that are almost the same, so your brain entertains them both and finds humor in the surprise that they both work. So I've told you about two thousand years of people making theories about humor. It's about superiority, it's about releasing tension, it's about play, it's about social bonding or linguistics or so on. And the thing to appreciate here is that these aren't mutually exclusive. Each of these theories has something to say about some element of humor, provide a different lens. And what this proliferation of theories really highlights is the multifaceted nature of humor and all the processes cognitive and emotional and social involved in finding something funny. So if you are that space alien, you'd find there's not just one single answer for your colleagues who are peppering you with questions and trying to understand earth humor. Instead, you'd have to come to the conclusion that there are many angles to this strange behavior. But we haven't even gotten to the best angle yet. I want to zoom in on one theory in particular that I think sits right at the center of much of comedy, and that has to do with the violation of expectation. The engine of most jokes involves setting up an expectation and then breaking it. Now, why does that work. It's because the brain is constantly predicting what it thinks is likely to happen, and in certain circumstances, when the next steps seem clear, but then they're suddenly violated, that's often funny. So this theory of humor is called incongruity theory, and the school of thought is favored by philosophers like Emmanuel Kant and Arthur Schopenhauer, and it suggests that humor arises when there's a discrepancy between what you think is about to happen and what actually happens. So let's take an example. I saw a post on social media yesterday that read, my husband and I have reached the difficult decision that we do not want children. If anybody does, send me your contact details and we can drop them off tomorrow. So your brain starts off with a particular understanding and then that's tripped up. Or here's another example. My dog used to chase people on bikes a lot. It got so bad that I finally had to take his bike away. Now, jokes like this work in part because language is so low bandwidth. When you hear the sentence, you're making lots of assumptions unconsciously under the hood without ever realizing it. Another example is the way that we predict words ahead of hearing them again without even realizing it. So any comedy can take advantage of that. So I can tell you last month I got diagnosed as being colorblind. That really came out of the orange. Now there's only a surprise there because your brain was predicting what it thought was going to come next. And this is the reason so many jokes are structured in patterns of threes. The first guy does something, and then the second guy establishes the pattern. Then your brain has a clear prediction for what the third guy is going to do, and the comedy comes when he breaks that pattern. So a structure of three is the fastest possible path to setting an expectation and then swerving off that road. And by the way, this issue about the brain setting expectations, this is something that you can start seeing in the first few months of life, even well before infants have language. You can study this, and that's because when an infant is surprised by something, they'll pay more attention to it. So, for example, you put a teddy bear behind a screen, and then you remove the screen and now there's a rabbit there. Even a very young infant will stare and stare at that, indicating that even though they can't speak to you yet, their brain had set up in expectation and the rabbit doesn't match it. One way that we know that comedy is about breaking expectations is because comedy has to surprise. Imagine that you're at a dinner party and the guy across from you tells a good joke and everybody laughs, and then he tells exactly the same joke a second time. It would be zero funny. The second time everyone would look at one another. So what does that tell us? That something funny has to surprise. So what we've seen so far is that humor has to betray your expectations. But I've left something out so far. There's another element to something being funny, because we quite often find that our expectations don't get fulfilled, and almost all of these situations aren't actually funny. Imagine you open your suitcase and you realize that you grabbed the wrong one at the airport. That would be surprising, Or an airplane engine suddenly falls onto the roof of your car. That would certainly violate your expectations, but it wouldn't be funny at all. So comedy requires a second element. It requires a sense of harmlessness. If some event or some punchline triggers fear or anxiety or disgust or whatever instead of amusement, it's not funny. Humor requires a very delicate balance of unexpected and harmless. And by the way, I should specify that this means a sense of harmlessness for the listener. There can be cruel jokes against other groups of people, out groups, and the jokes can involve bad things happening to them, But the idea is that the listener doesn't feel threatened. So if you are the space alien and you are being quizzed about what is required for human comedy, that's the main thing. It has to surprise and it has to not threaten the listener. And we'll come back to this in a few minutes, but first I want to mention that I was thinking about this harmlessness issue the other day and I realized this is consistent with something that I read from Woody Allen many years ago. He said, comedy equals tragedy plus time. In other words, events that are pain full or upsetting can over time become sources of humor. The time gives some emotional distance, so when something tragic first occurs, the emotions around it, like the grief and the anger and the shock, they're too raw for people to find anything funny about the situation. But as time passes, emotions tend to soften, the pain goes down, and people can look back on an event with a different mindset, and sometimes they see absurdities or ironies that weren't apparent before. So you and your partner lose your tempers about something because you said X and your partner thought you meant why, and you're both furious. But six months later you both love telling the story and you get comic value from it each time. And, by the way, comedians use this all the time to craft new material. The idea is that with just the right amount of time, this sting of some tragic event can fade enough that people can laugh at it without guilty or uncomfortable. But the time component is crucial because the comedian has to be sure that the audience is ready to find humor in the tragedy. In any case, time works because sometimes we have a perspective shift, we've changed how we collectively interpret the event, and sometimes it's just a coping mechanism. But in any case, this comes back to the point that humor can't be something that is directly threatening to us right now, So let's return to incongruity theory, which is that something funny has to violate your expectations. Now that's how this is thought about by philosophers. But now that neuroscience is on the scene, I think there's an even richer way to think about this. And this is something you hear me talk about on almost every episode. This is the issue of the internal model. So in the darkness of your skull, you have a model of what the world is and how it's working, and this is what gives you an understanding of what's going on out there, and it gives you your pre So imagine you hear a comedian tell his story. The comedian says, so I walked into the doctor's office and the doctor says to me, take off your clothes and put them there in the corner. Next to mine. Now, what the comedian's doing here is taking advantage of the assumptions of your internal model, the thoughts that went unthunk, even though they certainly could have been true that the doctor was naked, but they were never even considered until you were told that information, and then you have to retrospectively revise your whole model of that situation. Or take the joke I mentioned earlier about how my dog used to chase people on bikes a lot. Linguistically, this could have been interpreted by your brain as the dog riding the bike, and possibly some neurons in your brain entertain that relationship for a fraction of a second, but then they dismiss it, and so that unconscious possibility never even gets close to your consciousness until you suddenly have to do a wholesale go back to the beginning and re understand the whole situation. And by the way, while we're talking about subverting expectations, this is not just used by comedians, but also by mystery novelists and magicians. They all have something in common. They rely on surprising your internal model to entertain. So for the mystery novelists, it's the plot twist They set everything up for you, and if they're doing their job right, they know that all these clues can be scattered around you. But right now you think a particular model of the world is true, and then they surprise you by showing aha, all these things you saw are consistent with a different structure than the one you assumed, and with the magician, it's the same thing. They move their hands, they show you this, they draw your attention to that, and all along they are making sure that you believe a particular model of the world. They need you to believe that everything is operating one way, and then they violate your expectation. They flout your brain's predictions and leave you reveling in the mystery that one thing seemed true, but you're now looking at a different situation. And if you were that space alien trying to figure out humans, you'd probably notice that we spend a lot of our time flocking to mystery novelists and magicians and comedians. You would fly back to your planet and try to explain to your alien colleagues that humans continuously pay money to have these professionals give us some sort of story and then subvert our expectations. So why do we find this appealing. One possibility is that, as we're always trying to build a model of the world, we derive pleasure from the discovery of a flaw in our model. In other words, we are machines built to self correct, and it is rewarding to find an error and fix it. So part of the joy of humor is the feeling that you had a model and now you have a better one, a model that has more explanatory power. So in the three guys walk into a bar joke, the first guy sets an example, the second guy gets your internal model to believe that it understands a pattern, and then the third guy reveals there's a different way, a broader way that you could have understood the whole premise, I suggest we find it rewarding to change the internal model, and this is what solving riddles is about, or why people listen to science podcasts. There is some pleasure derived from the realization that your model was incomplete and now you see things with a broader view than you were able to just a moment ago. At its heart, I suggest that comedy is all about thinking that you have the world understood and then finding you didn't and you now have of a bigger model, and again when the change is harmless, not threatening, then we find it funny. Now, I want to take a one minute tangent here to tackle a question that I've been wondering about for a while. Can artificial intelligence be funny? And the answer to this, I think is very illuminating. On the one hand, AI can sometimes be hilarious and tell you great jokes, but this is because it is repeating or modifying a joke that has been said somewhere in the vast corpus of human writing, even if you've never heard it. A couple of episodes ago, I named this the intelligence echo illusion, by which I simply mean that we often mistake the echo of things that other people have said before for intelligence in AI, or in this case, for true comedy in AI. But it's nothing but repeat in any case. Although AI can repeat a good joke, what AI stinks at is making up an entirely new joke. I did some experiment to drill down on this. It's not because AI can't figure out what people expect next and then shift away from that. Instead, it's because a good joke has to replace the expectation with an alternative that also makes sense with a new frame. The punchline can't just be unexpected. Instead, it has to be cleverly engineered to have some second meaning, a second interpretation. So I'll give you an example that I just ran this morning. I didn't want chat gpt to tell me a joke i'd heard before, so I forced it to make up something new by prompting it to tell me a joke about lobsters and peanut butter. So here's what it came up with.

From the brain's point of view, What is humor when something is funny? Why do we breathe in and out rapidly? Do other animals laugh? Why do most jokes come in threes? What do mystery novelists, magicians and comedians have in common? And could AI be truly funny? Welcome to Inner Cosmos with me and David Eagleman. I'm a neuroscientist and author at Stanford and in these episodes we sail deeply into our three pound universe to understand why and how our lives look the way they do. Today's episode is about humor. Although humor is one of the most valued aspects of our lives, you've probably heard very little about it from the scientific point of view, and that changes today. So why do we laugh? After all? It's very strange behavior. Imagine that you are a space alien and you are studying humans. So through years of study, you note that humans seem to have a relatively high bandwidth channel of communication by an extraordinarily rapid and precise use of their larynx and their vocal cords. They move their tongue and their lips very rapidly. They blow air at just the right moments, and in this way they have language. They communicate to each other at about thirty nine bits per second, which is a pretty good transmission rate and way higher than any other animal species as far as you the alien can tell. But there's something else. These human creatures do something that's very strange. Every once in a while, they do a much lower frequency, lower bandwidth thing where they make a series of rhythmic, involuntary contractions of their diaphragm, which causes a sequence of vocalized exhalations, usually a series of short repeated vowel sounds like ha or he or ho. Now, you notice that this typically begins with some language or event that triggers the brain's reward centers and lights up something about the emotional networks, and that triggers the activation of facial muscles, particularly around the mouth and eyes, And often the human's mouth will open up wide and the corners of the lips will get drawn back and upward, and the respiratory starts doing these rapid cycles of inhalation and exhalation, which throws a wrench in the normal breathing patterns, and the heart rate increases and the blood pressure rises, and the eyes might start to produce tears, and the skin around the face might start turning red because of the increased blood flow. Sometimes the whole body shakes or quivers, especially in the shoulders and torso, and this physical manifestation that can spread to the limbs, leading to movements like clapping or slapping or bending over. Now, the question you ask as the alien is why do they do this strange laughing thing? Is there an evolutionary reason behind it? Do any other animals on the planet do it? So you go back to your alien university to present your findings, and the faculty there drills you with questions that you're supposed to know the answer to, like why do humans go to clubs and movies with the hopes that they will trigger a lot of these diaphragm contractions And if they get fewer contractions than expected, do they seem disappointed? Why do they get together with other humans that they trust to stick food in their mouths and hope to do these strange diaphragm contractions while eating, even though it's dangerous and could cause them to choke on their food. So we're going to take this in a few acts. First, we're going to address what is humor, And in the second act we'll ask why do we laugh? In other words, why do we do it out loud instead of silently. So let's start with the general notion of comedy about something being funny. As it turns out, people have been wondering about this for a long time, and the first known theories about humor go back to Plato. Now, Plato had a very dim view of laughter. He generally saw it as something malicious that people do. In his view, audiences laugh at people who have ignorance about themselves, who imagine themselves to be richer than they are, or better looking than they are, or more virtuous than they are, and we laugh at them, which he found to be a morally objectionable thing to do. Now, his student Aristotle appreciated wit in conversation, but he agreed with Plato that people laugh at the misfortunes or mistakes of others, which reinforces their own sense of self worth and status. Think of an audience laughing at a character in a comedy who's consistently making foolish mistakes. So this is what's known nowadays as superiority theory, and the idea is that comedy stems from feelings of being better than other people, and no one really challenged this idea that that's what comedy was about. Until the mid eighteenth century people started to think, wait a minute, you don't really need feelings of superiority to laugh at something. Just think of a funny poem or pun. And on the flip side, we often feel superior, like the way you might feel superior to a horse or a squirrel, but that doesn't mean we laugh at them. So other theories began to blossom, and now there are many theories of humor. One of them, for example, is relae theory. This was originally proposed by A Lord Shaftsbury in the seventeen fifties, and he suggested the slightly strange idea that we laugh to release animal spirits that have built up inside us. Now, this doesn't make much sense in our modern vocabulary, but later proponents of this idea, like Sigmund Freud and Herbert Spencer, they cast this same idea in a different light. They said, look, humor is a way to release psychological tension or suppressed emotions, like think of laughing at a joke that touches on a taboo subject. So laughter serves as a release valve for pent up energy in your nervous system, and in this view, it's a purely physiological issue. And you see this happen sometimes when someone laughs at a totally inappropriate moment, like someone has died, and the excess energy comes out in a way that looks different from what they're feeling internally. Relatedly, by the way, Freud also suggested that humor and laughter might act as a defense mechanism, and in this way it allows people to deal with uncomfortable emotions or social tensions, and it can reduce stress and anxiety. But there are other ways that people look at humor. One very common school of thought looks at humor as a way of indicating play. It says, look, play is absolutely essential for learning how to do real things in the world. And so the idea is that humor engages all this cognitive practice and social practice in a playful context. For example, look at the way that children engage in silly wordplay or crazy imaginative scenarios. That stuff cracks them up. They're playing. And there's a closely related way of looking at this too. When that evolutionary psychologists like the idea that humor and laughter is all about social bonding. Humor is a tool for strengthening the bonds within a group. You build cohesion this way, you build a sense of community. So just think about inside jokes that you do with your friends that reinforce your group identity and your camaraderie. And I think that the slang that each generation introduces is a form of the same thing, making sure that the adults are on the outside and you and your pals are on the inside. It's a way of bonding. Now, the ideas about humor don't end there. Other thinkers like Marvin Minsky and Jerry Saul's focus on a different aspect of humor, the cognitive aspect. They care about the mental processes involved in understanding and appreciating comedy. So they're looking at the cognitive effort required to understand some cognitive play on words. So take a joke like this today. I found a book with the title how to Solve fifty of Life's Problems, So I bought two of them. So the last sentence comes as a surprise, and the brain goes back and tries to reinterpret what it heard. There's a puzzle in there. Which forces you to reshape your interpretation, or specifically, your interpretation of the speaker's interpretation. And then it falls into place that there's another way to see this, and it strikes us as funny because it's both nonsensical and a little bit sensical. And some other theories zoom in even more on the types of humor that have to do with linguistics, in other words, about the structure and use of language, like wordplay or jokes that rely on double meanings like I'm addicted to break fluid, but it's okay because I can stop at any time, or jokes that rely on homophones, like a photon checks into a hotel, the front desk asks if it has any luggage and it says, no, Oh, I'm traveling light. So the punchline is a phrase that can be reinterpreted and has two meanings that surprisingly fit. Now, fundamentally, your brain is always trying to squeeze the complexity of the world down to a single interpretation. And something about the back and forth here between two interpretations that can both work makes something funny. Or take a kid's joke like why aren't lobsters generous because they're shellfish? This relies on two sounds that are almost the same, so your brain entertains them both and finds humor in the surprise that they both work. So I've told you about two thousand years of people making theories about humor. It's about superiority, it's about releasing tension, it's about play, it's about social bonding or linguistics or so on. And the thing to appreciate here is that these aren't mutually exclusive. Each of these theories has something to say about some element of humor, provide a different lens. And what this proliferation of theories really highlights is the multifaceted nature of humor and all the processes cognitive and emotional and social involved in finding something funny. So if you are that space alien, you'd find there's not just one single answer for your colleagues who are peppering you with questions and trying to understand earth humor. Instead, you'd have to come to the conclusion that there are many angles to this strange behavior. But we haven't even gotten to the best angle yet. I want to zoom in on one theory in particular that I think sits right at the center of much of comedy, and that has to do with the violation of expectation. The engine of most jokes involves setting up an expectation and then breaking it. Now, why does that work. It's because the brain is constantly predicting what it thinks is likely to happen, and in certain circumstances, when the next steps seem clear, but then they're suddenly violated, that's often funny. So this theory of humor is called incongruity theory, and the school of thought is favored by philosophers like Emmanuel Kant and Arthur Schopenhauer, and it suggests that humor arises when there's a discrepancy between what you think is about to happen and what actually happens. So let's take an example. I saw a post on social media yesterday that read, my husband and I have reached the difficult decision that we do not want children. If anybody does, send me your contact details and we can drop them off tomorrow. So your brain starts off with a particular understanding and then that's tripped up. Or here's another example. My dog used to chase people on bikes a lot. It got so bad that I finally had to take his bike away. Now, jokes like this work in part because language is so low bandwidth. When you hear the sentence, you're making lots of assumptions unconsciously under the hood without ever realizing it. Another example is the way that we predict words ahead of hearing them again without even realizing it. So any comedy can take advantage of that. So I can tell you last month I got diagnosed as being colorblind. That really came out of the orange. Now there's only a surprise there because your brain was predicting what it thought was going to come next. And this is the reason so many jokes are structured in patterns of threes. The first guy does something, and then the second guy establishes the pattern. Then your brain has a clear prediction for what the third guy is going to do, and the comedy comes when he breaks that pattern. So a structure of three is the fastest possible path to setting an expectation and then swerving off that road. And by the way, this issue about the brain setting expectations, this is something that you can start seeing in the first few months of life, even well before infants have language. You can study this, and that's because when an infant is surprised by something, they'll pay more attention to it. So, for example, you put a teddy bear behind a screen, and then you remove the screen and now there's a rabbit there. Even a very young infant will stare and stare at that, indicating that even though they can't speak to you yet, their brain had set up in expectation and the rabbit doesn't match it. One way that we know that comedy is about breaking expectations is because comedy has to surprise. Imagine that you're at a dinner party and the guy across from you tells a good joke and everybody laughs, and then he tells exactly the same joke a second time. It would be zero funny. The second time everyone would look at one another. So what does that tell us? That something funny has to surprise. So what we've seen so far is that humor has to betray your expectations. But I've left something out so far. There's another element to something being funny, because we quite often find that our expectations don't get fulfilled, and almost all of these situations aren't actually funny. Imagine you open your suitcase and you realize that you grabbed the wrong one at the airport. That would be surprising, Or an airplane engine suddenly falls onto the roof of your car. That would certainly violate your expectations, but it wouldn't be funny at all. So comedy requires a second element. It requires a sense of harmlessness. If some event or some punchline triggers fear or anxiety or disgust or whatever instead of amusement, it's not funny. Humor requires a very delicate balance of unexpected and harmless. And by the way, I should specify that this means a sense of harmlessness for the listener. There can be cruel jokes against other groups of people, out groups, and the jokes can involve bad things happening to them, But the idea is that the listener doesn't feel threatened. So if you are the space alien and you are being quizzed about what is required for human comedy, that's the main thing. It has to surprise and it has to not threaten the listener. And we'll come back to this in a few minutes, but first I want to mention that I was thinking about this harmlessness issue the other day and I realized this is consistent with something that I read from Woody Allen many years ago. He said, comedy equals tragedy plus time. In other words, events that are pain full or upsetting can over time become sources of humor. The time gives some emotional distance, so when something tragic first occurs, the emotions around it, like the grief and the anger and the shock, they're too raw for people to find anything funny about the situation. But as time passes, emotions tend to soften, the pain goes down, and people can look back on an event with a different mindset, and sometimes they see absurdities or ironies that weren't apparent before. So you and your partner lose your tempers about something because you said X and your partner thought you meant why, and you're both furious. But six months later you both love telling the story and you get comic value from it each time. And, by the way, comedians use this all the time to craft new material. The idea is that with just the right amount of time, this sting of some tragic event can fade enough that people can laugh at it without guilty or uncomfortable. But the time component is crucial because the comedian has to be sure that the audience is ready to find humor in the tragedy. In any case, time works because sometimes we have a perspective shift, we've changed how we collectively interpret the event, and sometimes it's just a coping mechanism. But in any case, this comes back to the point that humor can't be something that is directly threatening to us right now, So let's return to incongruity theory, which is that something funny has to violate your expectations. Now that's how this is thought about by philosophers. But now that neuroscience is on the scene, I think there's an even richer way to think about this. And this is something you hear me talk about on almost every episode. This is the issue of the internal model. So in the darkness of your skull, you have a model of what the world is and how it's working, and this is what gives you an understanding of what's going on out there, and it gives you your pre So imagine you hear a comedian tell his story. The comedian says, so I walked into the doctor's office and the doctor says to me, take off your clothes and put them there in the corner. Next to mine. Now, what the comedian's doing here is taking advantage of the assumptions of your internal model, the thoughts that went unthunk, even though they certainly could have been true that the doctor was naked, but they were never even considered until you were told that information, and then you have to retrospectively revise your whole model of that situation. Or take the joke I mentioned earlier about how my dog used to chase people on bikes a lot. Linguistically, this could have been interpreted by your brain as the dog riding the bike, and possibly some neurons in your brain entertain that relationship for a fraction of a second, but then they dismiss it, and so that unconscious possibility never even gets close to your consciousness until you suddenly have to do a wholesale go back to the beginning and re understand the whole situation. And by the way, while we're talking about subverting expectations, this is not just used by comedians, but also by mystery novelists and magicians. They all have something in common. They rely on surprising your internal model to entertain. So for the mystery novelists, it's the plot twist They set everything up for you, and if they're doing their job right, they know that all these clues can be scattered around you. But right now you think a particular model of the world is true, and then they surprise you by showing aha, all these things you saw are consistent with a different structure than the one you assumed, and with the magician, it's the same thing. They move their hands, they show you this, they draw your attention to that, and all along they are making sure that you believe a particular model of the world. They need you to believe that everything is operating one way, and then they violate your expectation. They flout your brain's predictions and leave you reveling in the mystery that one thing seemed true, but you're now looking at a different situation. And if you were that space alien trying to figure out humans, you'd probably notice that we spend a lot of our time flocking to mystery novelists and magicians and comedians. You would fly back to your planet and try to explain to your alien colleagues that humans continuously pay money to have these professionals give us some sort of story and then subvert our expectations. So why do we find this appealing. One possibility is that, as we're always trying to build a model of the world, we derive pleasure from the discovery of a flaw in our model. In other words, we are machines built to self correct, and it is rewarding to find an error and fix it. So part of the joy of humor is the feeling that you had a model and now you have a better one, a model that has more explanatory power. So in the three guys walk into a bar joke, the first guy sets an example, the second guy gets your internal model to believe that it understands a pattern, and then the third guy reveals there's a different way, a broader way that you could have understood the whole premise, I suggest we find it rewarding to change the internal model, and this is what solving riddles is about, or why people listen to science podcasts. There is some pleasure derived from the realization that your model was incomplete and now you see things with a broader view than you were able to just a moment ago. At its heart, I suggest that comedy is all about thinking that you have the world understood and then finding you didn't and you now have of a bigger model, and again when the change is harmless, not threatening, then we find it funny. Now, I want to take a one minute tangent here to tackle a question that I've been wondering about for a while. Can artificial intelligence be funny? And the answer to this, I think is very illuminating. On the one hand, AI can sometimes be hilarious and tell you great jokes, but this is because it is repeating or modifying a joke that has been said somewhere in the vast corpus of human writing, even if you've never heard it. A couple of episodes ago, I named this the intelligence echo illusion, by which I simply mean that we often mistake the echo of things that other people have said before for intelligence in AI, or in this case, for true comedy in AI. But it's nothing but repeat in any case. Although AI can repeat a good joke, what AI stinks at is making up an entirely new joke. I did some experiment to drill down on this. It's not because AI can't figure out what people expect next and then shift away from that. Instead, it's because a good joke has to replace the expectation with an alternative that also makes sense with a new frame. The punchline can't just be unexpected. Instead, it has to be cleverly engineered to have some second meaning, a second interpretation. So I'll give you an example that I just ran this morning. I didn't want chat gpt to tell me a joke i'd heard before, so I forced it to make up something new by prompting it to tell me a joke about lobsters and peanut butter. So here's what it came up with.

Three lobsters walk into a grocery store. The first lobster goes to the seafood section and asks for butter. The grocer gives him a tub of butter, and he happily scuttles away. The second lobster goes to the same section and asks for butter. The grocer gives him a tub of butter, and he too happily scuttles away. The third goes to the grocery stores pantry section and asks for peanut butter. The grocer looks surprised and asks why peanut butter. Aren't you going to cook with butter like the other lobsters. The third lobster replies, Nah, I'm allergic to butter, I always shell out for peanut butter instead.

Three lobsters walk into a grocery store. The first lobster goes to the seafood section and asks for butter. The grocer gives him a tub of butter, and he happily scuttles away. The second lobster goes to the same section and asks for butter. The grocer gives him a tub of butter, and he too happily scuttles away. The third goes to the grocery stores pantry section and asks for peanut butter. The grocer looks surprised and asks why peanut butter. Aren't you going to cook with butter like the other lobsters. The third lobster replies, Nah, I'm allergic to butter, I always shell out for peanut butter instead.

What now, I would call that the dumbest joke I've ever heard, But it doesn't even qualify as a joke. Why because the punchline, while it is a violation of expectation, doesn't offer a second interpretation that makes sense. So crafting a joke, at least for the moment, seems to be beyond the scope of large language models. They have no problem understanding that the structure of joke requires violating expectation, but they have no idea how to violate it. They don't know how to construct something that makes sense on two levels at the same time, which appears to be a requirement of humor. Now, let's return to the question that the space al asked at the beginning. Maybe it now understands why violations of expectation amuse humans as long as those violations are harmless. But why do humans engage in this very loud monkey call that they label laughter? And this is a good question because the alien notices that when you're having other emotions, you typically just experience them internally. When you're feeling shy, you don't do a high pitched yell when you're feeling morose. You don't sing and clap when you eat something and you find it delicious. You don't stand up in the restaurant and scream so that all the other diners know it. You simply experience emotions on the inside. So when we find something funny, why does that physically trigger these high amplitude, low frequency vocalizations. Why does your diaphragm contract over and over causing these rapid exhalations which cause your vocal cords to rapidly open and close create a loud sounds. Now, this is strange. Right to appreciate this, ask yourself a different kind of question. Why don't humans have the equivalent of a comedy club in the domain of beautiful art. Imagine you sit down at a museum with a lot of other people, and the mc brings out a wonderful painting for everyone to stare at, and then wheels out a beautiful statue, let's say, carved by Michaelangelo, and so on. You can't really imagine that you'd get a bunch of people physically making weird rhythmic sounds and filling the hall with noise. Instead, people go to museums and they quietly walk around and they're filled with a sense of beauty. But it's a private, quiet experience. So the question is why is laughter different? So in trying to understand this, one can ask the question of who else laughs? As in what other species? When we think about humans in relation to other species, we see that other species are collaborative and seem to have emotions like pain and hunger. But are they laughing? And the surprising answer is it appears some other animals do laugh, or at least they do things that are very similar to human laughter. For example, our primate friends, the chimpanzees and bonobo's and gorillas and orangutans make these vocalizations during play, and it seems to resemble the way that humans laugh. These sounds tend to be softer and more rhythmic compared to human laughter, but it appears to serve a similar function in social interactions. So here is an adolescent gorilla making these sounds when the zookeeper tickles his foot through the bars. A link the video on the show notes, and you can see the gorilla pulls his foot away when it tickles, but then he presents it again to be tickled. Another time, so you can hear these sounds during physical play like tickling or chasing, and the hypothesis is that it signals that the interaction is playful rather than aggressive. Almost all animals play because it helps them figure out how to get along with others and how to build skills that they're gonna need later, and so laughter is a broadcast signal to the others to say, this is not actually serious. This is play. In other words, I'm not actually trying to hurt you, and even though we're being physical and wrestling or whatever, I'm just trying to figure out what I will need later in life. And it's not just primates. You can also hear laughter in rats. They do this ultrasonic chirping at fifty killer hurts. This is really high frequency, so you can't hear this with your ears, but this can be measured with a microphone and then transferred to our range so we can hear it. And rat laughter sounds like this, And it turns out that rats do this when they play with each other and also when they are being tickled by humans. This seems to be a form of laughter, and it's associated with positive emotions and social bonding and By the way, rats that chirp more frequently tend to be more playful and sociable. And it's not just rats, but dogs also. They do something called play panting when they're doing social play, and some researchers think that this is like laughter. The dogs pant with this rhythmic, breathy sound, and they do this during playful interactions. But it's not because they're out of breath. It's that the signals to other dogs that their behavior is friendly and non threatening. And you know where else you find these physiologic signals that are like laughter dolphins. Dolphins do all kinds of vocalizations like whistles and clicks, and these seem to serve a similar function to laughter in terms of reinforcing social bonds and communication about what is the threat and what is not. So the latest estimate is that there are at least sixty five animal species who seem to laugh. And if you are the alien scientist, this is a really important clue. Essentially, in all these cases you detect the same general story that these laughter like sounds are employed to indicate that the behaviors are playful, they're not aggressive. In other words, I'm biting you, but I'm not really trying to hurt you. And across species you find that these laughter signals are used to strengthen social bonds and bring the group closer together. Okay, but the exact nature of laughter and animals may still be a little bit different from humans because we have our own evolutionary pathway. So why do we laugh while like our animal brethren, we laugh to indicate play, to tell the other this is not serious, and in humans this grows more subtle. We have more nuanced situations. So in human societies, if someone makes a social mistake, or someone finds themselves uncomfortable or risks someone else's standing, laughter is a broadcast signal to say, this is play, don't worry about it. And there's another suggestion too, made by my colleague Vs. Rahma Chandren in ninety eight, and he suggested that laughter is a way of alerting those around you that there's something dangerous, but it's no longer a threat. Essentially, laughter is like a monkey call that tells everyone else things are fine. It carries information that there has been a false alarm. So you see the man's ladder fall backwards and he lands on a haystack, and everyone needs to be alerted that he's okay, So you send out this call. If he hit rocks, nobody would laugh. On this note, I'll just mention I have a sort of painful memory from when I was ten years old and I was in a martial arts class and the instructor picked up a dumbbell with several plates on it, and he didn't realize that there wasn't a cuff on the end, and all the plates slipped off and almost landed on his foot but missed, and I laughed, and I got in trouble for it, and everyone thought it was deeply inappropriate. And the important part is that I felt terrible because I didn't find it funny. So I had no idea why that had come out of my mouth. But later I came to understand that laughter is an alerting system, and that gave me some insight into what had happened. I saw the plates slipping off, and I felt terrified, and then I saw that they all missed his foot by a few inches, and I was alerting the rest of the tribe that things were okay. I didn't expect people to laugh with me. I was simply communicating that things were not scary like we all thought for just a moment that they were about to be. Now, there are physical benefits to laughter. This may be true in animals too, but we really get this as humans. Laughter triggers the release of endorphins, which are natural painkillers and mood enhancers. So laughter reduces the perception of pain, improves overall pain tolerance, and it can improve mood. And it also improves immune function by increasing the production of antibodies and activating immune cells. And generally people find that it reduces the level of stress hormones like cortisol and adrenaline. So there are all kinds of cool things that laughter can do. But what I want to return to is the social aspect of it. And one of the things that's hard to miss is how laughter can be contagious. For example, go to YouTube to find a video of parrots laughing. They're just impersonating their human owners, but it is impossible to watch those videos and not laugh yourself. As I mentioned before, there are other weird cases where people laugh when they shouldn't, like when they hear some terrible news, because they just have too much emotion. Weirdly, this often has the property of becoming contagious. So someone hears something terrible and can't stop laughing, not because they believe it's funny, but because they have so much emotion that needs release. And what often happens is that the other people are horrified at first, but then they start laughing too, because it's very hard to help it. In fact, something I find fascinating is an expression that comedians say in private, which is that a comedian's two best friends are alcohol and density. Now the alcohol is obvious, but the density is worth unpacking. Comedians have always noted that if they get up to perform in front of a crowd of people who are spread out around the club, the exact same jokes aren't gonna go so well. They're not going to trigger the same laughter as they would if everyone was bunched up closely together. Why Because laughter spreads contagiously as long as everyone is sitting tightly packed. It's essentially impossible for someone to sit in the middle of a laughing crowd and not laugh themselves. Now again, evolutionary theorists argue that contagious laughter is a mechanism to foster a sense of unity in a group and that could help group survival. I'm not sure about the strength of that argument, because there are lots of ways that groups bond. Just look at something like fighting together. Look at the Spartans. They were tightly knit because they fought side by side and defended each other's lives. But I was thinking about this last night and it struck me that we don't really know if the Spartans were funny or not because they were such famous fighters. Maybe they were hilarious when they were sitting around the camp and eating dinner, and that's what caused the bonding. We just don't know. But the general are argument is that contagious laughter strengthens group cohesion. And by the way, there are other social aspects to laughter beyond contagion. One thing I find fascinating is laughter within hierarchies, where the person at the top laughs the loudest. The king and the plebeians don't laugh in the same way. You can see this clearly in very hierarchically structured cultures where laughter is used as a way to show deference or respect to authority figures, for example, laughing softly when superior makes a joke, even if it's not particularly funny as a way to show agreement. And this is actually a good segue because I've told you that when we look across the animal kingdom, we see there are several plausible evolutionary stories for thinking about laughter. But it's also worth noting that within the human species, there are several cultural variations the way that laughter is expressed and interpreted and used. It's not the same everywhere. For example, in Western cultures, laughter is generally associated with humor and used to express enjoyment or amusement or sarcasm. But in East Asian cultures, laughter is not only a response to humor but also a tool for managing social harmony. For example, in Japan, people might laugh softly or politely, even in awkward or uncomfortable situations, as a way to diffuse tension or to avoid conflict. And in Mediterranean cultures like in Italy and Greece, laughter tends to be more exuberant and loud, and it often accompanies animated conversations and it's seen as a sign of enthusiasm and engagement, Whereas in Scandinavian cultures like Sweden and Norway, laughter tends to be more subdued and controlled and loud laughter can be perceived as inappropriate, and there are gender differences. In some Middle Eastern cultures, men and women are expected to laugh differently. Women are typically expected to laugh more softly or modestly in public, whereas men are free to laugh loudly. In Western societies, while there are no strict rules, studies show that women tend to laugh more frequently than men at social settings, often as a way of facilitating social interaction, and by the way, the responses to laughter can also be different. Just as an example, in Eastern European cultures like Russia, laughter informal or serious contexts is viewed as inappropriate and with suspicion, and what's done instead of laughter is a quick or reserved smile, especially in professional settings. But contrast this with Latin American cultures, where laughter is generally more freely expressed and is a key part of social interactions. People laugh easily in everyday conversations and they use it as a way to express warmth and friendliness. So laughter is a common human experience, but it does get molded a bit by cultural norms and values. Let's wrap up today's podcast. If you are the space Alien and you have to go home to explain to your colleagues what human laughter is about. You're going to find there's not just one answer why, because there are many different flavors of humor, from laughing at someone to laughing with someone, to laughing at clever wordplay with two meanings. And there's the kind of laughter where you are appreciating masterful violation of expectation. And physically, there are different kinds of laughter. Some humans have a quick contraction of the diaphragm and they make a snort, or you might find the unrestrained burst of laughter that we call a guffaw fully engaging the respiratory muscles. Or you might hear the puckish glee of a cackle, which is sharp and high pitched, with rapid, irregular exhalations from the lungs. Or you might spot the contentment of a chuckle, which is low pitched and sustained, involving rhythmic contractions of the diaphragm and the soft vocalizations. Or you might catch the slyness of a snicker, or the innocence of a high pitched giggle, or the thunderous roll of a belly laugh that deep, full bodied contraction of the abdominal muscles. So if you're the space alien, you'd have to conclude that humans seem to laugh for a variety of reasons in a variety of ways, and it's not as low bandwidth as you thought. In different circumstances, it can signal play, it can strengthen social bonds, it can reduce tensions, it can give emotional release, and it can communicate. It can nonverbally broadcast amusement or agreement or discomfort or false alarms. So while the alien and its compatriots might be confused, we don't care because we love to laugh. We have millions of years and billions of neurons behind it, all pushing us towards mirth. Until next time, may your neural path ways continue to be tickled. Go to Eagleman dot com slash podcast for more information and to find lots of reading about the science of humor. Send me an email at podcast at eagleman dot com with questions or discussion and check out. Subscribe to Inner Cosmos on YouTube for videos of each episode and to leave comments. Until next time. I'm David Eagleman, and this is Inner Cosmos.

What now, I would call that the dumbest joke I've ever heard, But it doesn't even qualify as a joke. Why because the punchline, while it is a violation of expectation, doesn't offer a second interpretation that makes sense. So crafting a joke, at least for the moment, seems to be beyond the scope of large language models. They have no problem understanding that the structure of joke requires violating expectation, but they have no idea how to violate it. They don't know how to construct something that makes sense on two levels at the same time, which appears to be a requirement of humor. Now, let's return to the question that the space al asked at the beginning. Maybe it now understands why violations of expectation amuse humans as long as those violations are harmless. But why do humans engage in this very loud monkey call that they label laughter? And this is a good question because the alien notices that when you're having other emotions, you typically just experience them internally. When you're feeling shy, you don't do a high pitched yell when you're feeling morose. You don't sing and clap when you eat something and you find it delicious. You don't stand up in the restaurant and scream so that all the other diners know it. You simply experience emotions on the inside. So when we find something funny, why does that physically trigger these high amplitude, low frequency vocalizations. Why does your diaphragm contract over and over causing these rapid exhalations which cause your vocal cords to rapidly open and close create a loud sounds. Now, this is strange. Right to appreciate this, ask yourself a different kind of question. Why don't humans have the equivalent of a comedy club in the domain of beautiful art. Imagine you sit down at a museum with a lot of other people, and the mc brings out a wonderful painting for everyone to stare at, and then wheels out a beautiful statue, let's say, carved by Michaelangelo, and so on. You can't really imagine that you'd get a bunch of people physically making weird rhythmic sounds and filling the hall with noise. Instead, people go to museums and they quietly walk around and they're filled with a sense of beauty. But it's a private, quiet experience. So the question is why is laughter different? So in trying to understand this, one can ask the question of who else laughs? As in what other species? When we think about humans in relation to other species, we see that other species are collaborative and seem to have emotions like pain and hunger. But are they laughing? And the surprising answer is it appears some other animals do laugh, or at least they do things that are very similar to human laughter. For example, our primate friends, the chimpanzees and bonobo's and gorillas and orangutans make these vocalizations during play, and it seems to resemble the way that humans laugh. These sounds tend to be softer and more rhythmic compared to human laughter, but it appears to serve a similar function in social interactions. So here is an adolescent gorilla making these sounds when the zookeeper tickles his foot through the bars. A link the video on the show notes, and you can see the gorilla pulls his foot away when it tickles, but then he presents it again to be tickled. Another time, so you can hear these sounds during physical play like tickling or chasing, and the hypothesis is that it signals that the interaction is playful rather than aggressive. Almost all animals play because it helps them figure out how to get along with others and how to build skills that they're gonna need later, and so laughter is a broadcast signal to the others to say, this is not actually serious. This is play. In other words, I'm not actually trying to hurt you, and even though we're being physical and wrestling or whatever, I'm just trying to figure out what I will need later in life. And it's not just primates. You can also hear laughter in rats. They do this ultrasonic chirping at fifty killer hurts. This is really high frequency, so you can't hear this with your ears, but this can be measured with a microphone and then transferred to our range so we can hear it. And rat laughter sounds like this, And it turns out that rats do this when they play with each other and also when they are being tickled by humans. This seems to be a form of laughter, and it's associated with positive emotions and social bonding and By the way, rats that chirp more frequently tend to be more playful and sociable. And it's not just rats, but dogs also. They do something called play panting when they're doing social play, and some researchers think that this is like laughter. The dogs pant with this rhythmic, breathy sound, and they do this during playful interactions. But it's not because they're out of breath. It's that the signals to other dogs that their behavior is friendly and non threatening. And you know where else you find these physiologic signals that are like laughter dolphins. Dolphins do all kinds of vocalizations like whistles and clicks, and these seem to serve a similar function to laughter in terms of reinforcing social bonds and communication about what is the threat and what is not. So the latest estimate is that there are at least sixty five animal species who seem to laugh. And if you are the alien scientist, this is a really important clue. Essentially, in all these cases you detect the same general story that these laughter like sounds are employed to indicate that the behaviors are playful, they're not aggressive. In other words, I'm biting you, but I'm not really trying to hurt you. And across species you find that these laughter signals are used to strengthen social bonds and bring the group closer together. Okay, but the exact nature of laughter and animals may still be a little bit different from humans because we have our own evolutionary pathway. So why do we laugh while like our animal brethren, we laugh to indicate play, to tell the other this is not serious, and in humans this grows more subtle. We have more nuanced situations. So in human societies, if someone makes a social mistake, or someone finds themselves uncomfortable or risks someone else's standing, laughter is a broadcast signal to say, this is play, don't worry about it. And there's another suggestion too, made by my colleague Vs. Rahma Chandren in ninety eight, and he suggested that laughter is a way of alerting those around you that there's something dangerous, but it's no longer a threat. Essentially, laughter is like a monkey call that tells everyone else things are fine. It carries information that there has been a false alarm. So you see the man's ladder fall backwards and he lands on a haystack, and everyone needs to be alerted that he's okay, So you send out this call. If he hit rocks, nobody would laugh. On this note, I'll just mention I have a sort of painful memory from when I was ten years old and I was in a martial arts class and the instructor picked up a dumbbell with several plates on it, and he didn't realize that there wasn't a cuff on the end, and all the plates slipped off and almost landed on his foot but missed, and I laughed, and I got in trouble for it, and everyone thought it was deeply inappropriate. And the important part is that I felt terrible because I didn't find it funny. So I had no idea why that had come out of my mouth. But later I came to understand that laughter is an alerting system, and that gave me some insight into what had happened. I saw the plates slipping off, and I felt terrified, and then I saw that they all missed his foot by a few inches, and I was alerting the rest of the tribe that things were okay. I didn't expect people to laugh with me. I was simply communicating that things were not scary like we all thought for just a moment that they were about to be. Now, there are physical benefits to laughter. This may be true in animals too, but we really get this as humans. Laughter triggers the release of endorphins, which are natural painkillers and mood enhancers. So laughter reduces the perception of pain, improves overall pain tolerance, and it can improve mood. And it also improves immune function by increasing the production of antibodies and activating immune cells. And generally people find that it reduces the level of stress hormones like cortisol and adrenaline. So there are all kinds of cool things that laughter can do. But what I want to return to is the social aspect of it. And one of the things that's hard to miss is how laughter can be contagious. For example, go to YouTube to find a video of parrots laughing. They're just impersonating their human owners, but it is impossible to watch those videos and not laugh yourself. As I mentioned before, there are other weird cases where people laugh when they shouldn't, like when they hear some terrible news, because they just have too much emotion. Weirdly, this often has the property of becoming contagious. So someone hears something terrible and can't stop laughing, not because they believe it's funny, but because they have so much emotion that needs release. And what often happens is that the other people are horrified at first, but then they start laughing too, because it's very hard to help it. In fact, something I find fascinating is an expression that comedians say in private, which is that a comedian's two best friends are alcohol and density. Now the alcohol is obvious, but the density is worth unpacking. Comedians have always noted that if they get up to perform in front of a crowd of people who are spread out around the club, the exact same jokes aren't gonna go so well. They're not going to trigger the same laughter as they would if everyone was bunched up closely together. Why Because laughter spreads contagiously as long as everyone is sitting tightly packed. It's essentially impossible for someone to sit in the middle of a laughing crowd and not laugh themselves. Now again, evolutionary theorists argue that contagious laughter is a mechanism to foster a sense of unity in a group and that could help group survival. I'm not sure about the strength of that argument, because there are lots of ways that groups bond. Just look at something like fighting together. Look at the Spartans. They were tightly knit because they fought side by side and defended each other's lives. But I was thinking about this last night and it struck me that we don't really know if the Spartans were funny or not because they were such famous fighters. Maybe they were hilarious when they were sitting around the camp and eating dinner, and that's what caused the bonding. We just don't know. But the general are argument is that contagious laughter strengthens group cohesion. And by the way, there are other social aspects to laughter beyond contagion. One thing I find fascinating is laughter within hierarchies, where the person at the top laughs the loudest. The king and the plebeians don't laugh in the same way. You can see this clearly in very hierarchically structured cultures where laughter is used as a way to show deference or respect to authority figures, for example, laughing softly when superior makes a joke, even if it's not particularly funny as a way to show agreement. And this is actually a good segue because I've told you that when we look across the animal kingdom, we see there are several plausible evolutionary stories for thinking about laughter. But it's also worth noting that within the human species, there are several cultural variations the way that laughter is expressed and interpreted and used. It's not the same everywhere. For example, in Western cultures, laughter is generally associated with humor and used to express enjoyment or amusement or sarcasm. But in East Asian cultures, laughter is not only a response to humor but also a tool for managing social harmony. For example, in Japan, people might laugh softly or politely, even in awkward or uncomfortable situations, as a way to diffuse tension or to avoid conflict. And in Mediterranean cultures like in Italy and Greece, laughter tends to be more exuberant and loud, and it often accompanies animated conversations and it's seen as a sign of enthusiasm and engagement, Whereas in Scandinavian cultures like Sweden and Norway, laughter tends to be more subdued and controlled and loud laughter can be perceived as inappropriate, and there are gender differences. In some Middle Eastern cultures, men and women are expected to laugh differently. Women are typically expected to laugh more softly or modestly in public, whereas men are free to laugh loudly. In Western societies, while there are no strict rules, studies show that women tend to laugh more frequently than men at social settings, often as a way of facilitating social interaction, and by the way, the responses to laughter can also be different. Just as an example, in Eastern European cultures like Russia, laughter informal or serious contexts is viewed as inappropriate and with suspicion, and what's done instead of laughter is a quick or reserved smile, especially in professional settings. But contrast this with Latin American cultures, where laughter is generally more freely expressed and is a key part of social interactions. People laugh easily in everyday conversations and they use it as a way to express warmth and friendliness. So laughter is a common human experience, but it does get molded a bit by cultural norms and values. Let's wrap up today's podcast. If you are the space Alien and you have to go home to explain to your colleagues what human laughter is about. You're going to find there's not just one answer why, because there are many different flavors of humor, from laughing at someone to laughing with someone, to laughing at clever wordplay with two meanings. And there's the kind of laughter where you are appreciating masterful violation of expectation. And physically, there are different kinds of laughter. Some humans have a quick contraction of the diaphragm and they make a snort, or you might find the unrestrained burst of laughter that we call a guffaw fully engaging the respiratory muscles. Or you might hear the puckish glee of a cackle, which is sharp and high pitched, with rapid, irregular exhalations from the lungs. Or you might spot the contentment of a chuckle, which is low pitched and sustained, involving rhythmic contractions of the diaphragm and the soft vocalizations. Or you might catch the slyness of a snicker, or the innocence of a high pitched giggle, or the thunderous roll of a belly laugh that deep, full bodied contraction of the abdominal muscles. So if you're the space alien, you'd have to conclude that humans seem to laugh for a variety of reasons in a variety of ways, and it's not as low bandwidth as you thought. In different circumstances, it can signal play, it can strengthen social bonds, it can reduce tensions, it can give emotional release, and it can communicate. It can nonverbally broadcast amusement or agreement or discomfort or false alarms. So while the alien and its compatriots might be confused, we don't care because we love to laugh. We have millions of years and billions of neurons behind it, all pushing us towards mirth. Until next time, may your neural path ways continue to be tickled. Go to Eagleman dot com slash podcast for more information and to find lots of reading about the science of humor. Send me an email at podcast at eagleman dot com with questions or discussion and check out. Subscribe to Inner Cosmos on YouTube for videos of each episode and to leave comments. Until next time. I'm David Eagleman, and this is Inner Cosmos.